1. Field of the Invention
The present invention relates to a solar simulator and a method for driving the same. In particular, the present invention relates to a solar simulator for generating light from a xenon arc lamp, which is preferable in measurement of the output characteristic of photovoltaic devices, as pseudo sunlight, and also to a method for driving such a solar simulator.
2. Description of the Related Art
As the importance of photovoltaic devices as clean energy is being widely recognized, the demand for such devices is increasing. The demand is coming from a variety of fields, from power energy supplies for large-scale machines to small-scale power supplies for precise electronic machines.
Here, in order for photovoltaic devices to be widely used in a variety of fields, accurate measurement of the characteristics, in particular, the output characteristic, of the photovoltaic devices is necessary, as many problems would otherwise be expected to arise where the photovoltaic devices is used. Therefore, conventionally, a solar simulator for measuring the output characteristic of photovoltaic devices has been proposed, and actually used (see Japanese Patent Publication No. Hei 6-105280).
When the output characteristic of photovoltaic devices is measured using such a solar simulator, in particular, when the output characteristic of large-scaled photovoltaic devices having the size (the area of an test plane) of 1 m×1 m or larger is measured, for example, it is necessary to use a solar simulator having a plurality of xenon arc lamps arranged therein. That is, where the amount of light emitted from a single xenon arc lamp presents the irradiance distribution schematically shown in FIG. 9, it is necessary to ensure uniform illumination over the test plane of the solar simulator used in the measurement by using a plurality of xenon arc lamps.
In addition, there are a variety of shapes (external shape) available, including a shape that is long in the lateral direction, as the shape of large-scaled photovoltaic devices, and with respect to large-scale photovoltaic devices having the size of 1 m×4 m, for example, a solar simulator having two xenon arc lamps each about 2,000 mm long arranged therein is used for the measurement of the output characteristic thereof.
In FIG. 9, XL refers to a xenon arc lamp, Lx and Ly refer to the waveforms indicative of the light amount along the x-axis and the y-axis, respectively, and Sb refers to photovoltaic devices to be measured.
However, a solar simulator having a plurality of xenon arc lamps as a light source suffers from a problem that an expected amount of light is not readily and stably obtained from each xenon arc lamp and therefore uniform irradiance over the test plane is not readily ensured.
As for the light emission circuit of a conventional solar simulator which has xenon lamps as a light source, when the solar simulator is constructed having a plurality of xenon lamps to produce light emission therefrom, a problem is expected in that the entire structure is resultantly enlarged as such a light emission circuit (in particular, a power supply device contained therein) is provided for each lamp and therefore a large space within the solar simulator is occupied by the light emission circuits.
Provision of an individual light emission circuit for each lamp leads to another problem that uniform irradiance is not readily ensured over the test plane relative to large-scale photovoltaic devices as the amount of light irradiated from each of the lamps may vary as time passes.
Here, a capacitor used as a power supply of a solar simulator in which a single light emission circuit is used to produce light emission from a single lamp is required to have comparable withstand voltage and a commercially available typical capacitor having such a withstand voltage is of a few μF to a few tens of μF. Therefore, when such a commercially available capacitor is used, the produced light emission can last at most for about 1 millisecond.
Moreover, as the amount of light emitted from the xenon arc lamp may vary when the capacitor discharges, depending on the voltage variation according to the discharge curve of the capacitor, this also makes it difficult to stably obtain a constant amount of light. In actual fact, in measurement of the output characteristic of photovoltaic devices, light emission is attempted from a few tens of times to about one hundred and thirty times for a single photovoltaic devices to be measured.
Therefore, in such a situation, it is more difficult, or sometimes even impossible using a conventional technique, to ensure uniform irradiance when the output characteristic of large-scale photovoltaic devices is measured while producing light emission from a plurality of lamps.
In measurement of the output characteristic of photovoltaic devices which is slow in response, light emission is required to be continued for from a few hundred microseconds to a few seconds. A light emission circuit capable of such prolonged light emission is constructed having a main discharge voltage supply prepared in the form of a large-scale high capacity power supply.
Here, suppose that the light source lamp is a xenon arc lamp in which discharge electrodes are situated apart from each other by a distance of about 1000 mm, for example, an electrical potential of about 2000 V to 3000 V is required, and a current of about 30 A flows in the main discharge. A power supply which meets the specifications of this high electrical potential and current is a large-scale power supply of about 60 KW to 90 KW.
Therefore, a conventional light emission circuit capable of measuring the output characteristic of large-scale photovoltaic devices, which requires light emission from a plurality of lamps, inevitably has a large-scale power supply device. As a result, the solar simulator is resultantly enlarged with related device cost accordingly increased.